A business analyst is responsible for understanding business needs, analysing problems, eliciting requirements, exploring options, and helping stakeholders define valuable change. Options A, B, and D are all normal business analysis responsibilities. The analyst investigates the business situation, identifies needs, supports option development, and uses elicitation techniques such as interviews, workshops, observation, and document analysis to understand requirements. Ensuring that projects are delivered within budget constraints is primarily a project management responsibility. A project manager controls project delivery, manages schedule, cost, resources, risks, and progress against the approved plan. The business analyst may contribute estimates or impact analysis, but they do not normally own budget delivery. Therefore, option C is least likely to be a business analyst responsibility.